More studies needed on oregano’s effects

DEAR DOCTOR: What are the benefits of oregano oil?

DEAR READER: Oregano is well-known for its culinary versatility, but it has purported health benefits as well. A native of the Mediterranean region, the plant was used by the ancient Greek physician Hippocrates as an antiseptic and as an aid for digestive and respiratory ailments.

The beneficial effects of oregano appear to be from two specific chemical compounds, carvacrol and thymol. Both have been shown to have activity against multiple bacteria in laboratory settings. Among the many subspecies of oregano, all of them contain these two compounds — known as phenols — in some proportion. Oregano contains other phenol compounds as well, potentially boosting its antibacterial effects.

These compounds could be at least part of the reason why both the oregano plant and oregano oil inhibit the replication of intestinal pathogenic bacteria, such as Escherichia coli, Bacillus cereus and Salmonella, as well as the respiratory pathogens Strep. pyogenes,

Staph. aureus and Moraxella. Also, oregano alone and carvacrol alone have shown activity against the norovirus, which causes gastrointestinal illnesses.

As for whether this anti-microbial effect translates to the world outside of a petri dish, only one good human study shows any efficacy. A 2017 study in the European Journal of Nutrition looked at rats that were given medications to induce breast cancer. But again, human studies are virtually nonexistent.

Some people report nausea and bloating with oregano oil, but overall, it appears safe. A 90-day study of oregano oil in rats found no adverse effects.

As for whether oregano oil has benefits, the answer is a solid maybe. No controlled human trials can even say whether it’s effective against either infection or cancer. Some of the individual components such as carvacrol and thymol should be further studied in humans.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the UCLA.

Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA 90095.